Polyamide composite structures and processes for their preparation

ABSTRACT

Disclosed herein are polyamide composite structures and processes for their preparation. The disclosed composite structures comprise a surface, having at least a portion made of a surface resin composition, and comprise a fibrous material being impregnated with a matrix resin composition. The surface resin composition is selected from polyamide compositions comprising a blend of (A) fully aliphatic polyamides having a melting point of less than 230° C., and (B) fully aliphatic polyamides having a melting point of at least 250° C., and wherein the matrix resin composition is independently selected from (B) or blends of (A) and (B).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 61/408,166, filed Oct. 29, 2010, which is now pending,the entire disclosure of which is incorporated herein by reference; andU.S. Provisional Application Nos. 61/410,093, filed Nov. 4, 2010;61/410,100, filed Nov. 4, 2010; 61/410,104, filed Nov. 4, 2010; and61/410,108, filed Nov. 4, 2010, all of which are now pending, the entiredisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of composite structures andprocesses for their preparation, particularly it relates to the field ofpolyamide composite structures.

BACKGROUND OF THE INVENTION

With the aim of replacing metal parts for weight saving and costreduction while having comparable or superior mechanical performance,structures based on composite materials comprising a polymer matrixcontaining a fibrous material have been developed. With this growinginterest, fiber reinforced plastic composite structures have beendesigned because of their excellent physical properties resulting fromthe combination of the fibrous material and the polymer matrix and areused in various end-use applications. Manufacturing techniques have beendeveloped for improving the impregnation of the fibrous material with apolymer matrix to optimize the properties of the composite structure.

In highly demanding applications, such as for example structural partsin automotive and aerospace applications, composite materials aredesired due to a unique combination of lightweight, high strength andtemperature resistance.

High performance composite structures can be obtained usingthermosetting resins or thermoplastic resins as the polymer matrix.Thermoplastic-based composite structures present several advantages overthermoset-based composite structures such as, for example, the fact thatthey can be post-formed or reprocessed by the application of heat andpressure, that a reduced time is needed to make the composite structuresbecause no curing step is required, and their increased potential forrecycling. Indeed, the time consuming chemical reaction of cross-linkingfor thermosetting resins (curing) is not required during the processingof thermoplastics. Among thermoplastic resins, polyamides areparticularly well suited for manufacturing composite structures.Thermoplastic polyamide compositions are desirable for use in a widerange of applications including parts used in automobiles,electrical/electronic parts, household appliances and furniture becauseof their good mechanical properties, heat resistance, impact resistanceand chemical resistance and because they may be conveniently andflexibly molded into a variety of articles of varying degrees ofcomplexity and intricacy.

U.S. Pat. No. 4,255,219 discloses a thermoplastic sheet material usefulin forming composites. The disclosed thermoplastic sheet material ismade of polyamide 6 and a dibasic carboxylic acid or anhydride or estersthereof and at least one reinforcing mat of long glass fibers encasedwithin said layer.

For making integrated composite structures and to increase theperformance of polymers, it is often desired to “overmold” one or moreparts made of a polymer onto a portion or all of the surfaces of acomposite structure so as to surround or encapsulate said surfaces.Overmolding involves shaping, e.g. by injection molding, a secondpolymer part directly onto at least a portion of one or more surfaces ofthe composite structure, to form a two-part composite structure, whereinthe two parts are adhered one to the other at least at one interface.The polymer compositions used to impregnate the fibrous material (i.e.the matrix polymer composition) and the polymer compositions used toovermold the impregnated fibrous material (i.e. the overmolding polymercomposition) are desired to have good adhesion one to the other,extremely good dimensional stability and retain their mechanicalproperties under adverse conditions, including thermal cycling, so thatthe composite structure is protected under operating conditions and thushas an increased lifetime.

Unfortunately, conventional thermoplastic polyamide resin compositionsthat are used to impregnate one or more fibrous layers and to overmoldthe one or more impregnated fibrous layers may require excessive heatingduring stamping, forming, or shaping, which may render their surfacespoor in appearance and in functionality, and/or may show poor adhesionbetween the overmolded polymer and the surface of the componentcomprising the fibrous material, i.e. the composite structure. The pooradhesion may result in the formation of cracks at the interface of theovermolded composite structures leading to reduced mechanicalproperties, premature aging and problems related to delamination anddeterioration of the article upon use and time.

In such case of weak adhesion, the interface between the compositestructure and the overmolding resin will break first, rendering theovermolded composite structure weaker than either of its components.Therefore, high adhesion strength between the components is highlydesirable. However, once the bonding strength is high enough that theinterface can sustain the applied load without being the first to break,yet higher mechanical performance of the structure is highly desirableas is needed for the most highly demanding applications. Lowermechanical performance in these most demanding applications may impairthe durability and safety of the article upon use and time. Flexuralstrength, i.e. the maximum flexural stress sustained by the testspecimen during a bending test, is commonly used as an indication of amaterial's ability to bear (or to sustain, or to support) load whenflexed. When overmolding a resin composition onto at least a portion ofa composite structure, high mechanical performance such as flexuralstrength of the structure is desired beyond that realized by goodbonding strength between the composite structure and the overmoldingresin.

There is a need for a thermoplastic polyamide composite structure thatis easier to process in forming, shaping, or stamping, that exhibitsgood mechanical properties, especially flexural strength and having atleast a portion of its surface allowing a good adhesion between itssurface and an overmolding resin comprising a polyamide resin.

SUMMARY OF THE INVENTION

Described herein is a composite structure having a surface, whichsurface has at least a portion made of a surface resin composition, andcomprising a fibrous material selected from non-woven structures,textiles, fibrous battings and combinations thereof, said fibrousmaterial being impregnated with a matrix resin composition, wherein thesurface resin composition is selected from polyamide compositionscomprising a blend of (A) one or more fully aliphatic polyamidesselected from group (I) polyamides having a melting point of less than230° C., and (B) one or more fully aliphatic polyamides selected fromgroup (II) polyamides having a melting point of at least 250° C., andwherein the matrix resin composition is independently selected from (B)or independently selected from blends of (A) and (B).

Further described herein is a process for making the composite structuredescribed above. The process for making the composite structuredescribed above comprises a step of i) impregnating with the matrixresin composition the fibrous material, wherein at least a portion ofthe surface of the composite structure is made of the surface resincomposition.

DETAILED DESCRIPTION

The composite structure according to the present invention has improvedimpact resistance and flexural strength and allows a good adhesion whena part made of an overmolding resin composition comprising athermoplastic polyamide is adhered onto at least a portion of thesurface of the composite structure. A good impact resistance andflexural strength of the composite structure and a good adhesion betweenthe composite structure and the overmolding resin leads to structuresexhibiting good resistance to deterioration and resistance todelamination of the structure with use and time.

Several patents and publications are cited in this description. Theentire disclosure of each of these patents and publications isincorporated herein by reference.

As used herein, the term “a” refers to one as well as to at least oneand is not an article that necessarily limits its referent noun to thesingular.

As used herein, the terms “about” and “at or about” are intended to meanthat the amount or value in question may be the value designated or someother value about the same. The phrase is intended to convey thatsimilar values promote equivalent results or effects according to theinvention.

As used herein, the term “melting point” in reference to a polyamiderefers to the melting point of the pure resin as determined withdifferential scanning calorimetry (DSC) at a scan rate of 10° C./min inthe first heating scan, wherein the melting point is taken at themaximum of the endothermic peak. In customary measurements of meltingbehavior of blends of polymers, more than one heating scans may beperformed on a single specimen, and the second and/or later scans mayshow a different melting behavior from the first scan. This differentmelting behavior may be observed as a shift in temperature of themaximum of the endothermic peak and/or as a broadening of the meltingpeak with possibly more than one peaks, which may be an effect ofpossible transamidation in the case of more than one polyamides.However, when selecting polyamides for Group I or for Group IIpolyamides in the scope of the current invention, always the peak of themelting endotherm of the first heating scan of the single polyamide isused. As used herein, a scan rate is an increase of temperature per unittime. Sufficient energy must be supplied to maintain a constant scanrate of 10° C./min until a temperature of at least 30° C. and preferablyat least 50° C. above the melting point is reached.

The present invention comprises a fibrous material that is impregnatedwith a matrix resin composition. At least a portion of the surface ofthe composite structure is made of a surface resin composition. Thematrix resin composition and the surface resin composition may beidentical or may be different.

As used herein, the term “a fibrous material being impregnated with amatrix resin composition” means that the matrix resin compositionencapsulates and embeds the fibrous material so as to form aninterpenetrating network of fibrous material substantially surrounded bythe matrix resin composition. For purposes herein, the term “fiber”refers to a macroscopically homogeneous body having a high ratio oflength to width across its cross-sectional area perpendicular to itslength. The fiber cross section can be any shape, but is typicallyround. The fibrous material may be in any suitable form known to thoseskilled in the art and is preferably selected from non-woven structures,textiles, fibrous battings and combinations thereof. Non-wovenstructures can be selected from random fiber orientation and alignedfibrous structures. Examples of random fiber orientation include withoutlimitation chopped and continuous material which can be in the form of amat, a needled mat or a felt. Examples of aligned fibrous structuresinclude without limitation unidirectional fiber strands, bidirectionalstrands, multidirectional strands, multi-axial textiles. Textiles can beselected from woven forms, knits, braids and combinations thereof. Thefibrous material can be continuous or discontinuous in form.

Depending on the end-use application of the composite structure and therequired mechanical properties, more than one fibrous materials can beused, either by using several same fibrous materials or a combination ofdifferent fibrous materials, i.e. the first component described hereinmay comprise one or more fibrous materials. An example of a combinationof different fibrous materials is a combination comprising a non-wovenstructure such as for example a planar random mat which is placed as acentral layer and one or more woven continuous fibrous materials thatare placed as outside layers. Such a combination allows an improvementof the processing and thereof of the homogeneity of the first componentthus leading to improved mechanical properties. The fibrous material maybe made of any suitable material or a mixture of materials provided thatthe material or the mixture of materials withstand the processingconditions used during impregnation by the matrix resin composition andthe surface resin composition.

Preferably, the fibrous material comprises glass fibers, carbon fibers,aramid fibers, graphite fibers, metal fibers, ceramic fibers, naturalfibers or mixtures thereof; more preferably, the fibrous materialcomprises glass fibers, carbon fibers, aramid fibers, natural fibers ormixtures thereof; and still more preferably, the fibrous materialcomprises glass fibers, carbon fibers and aramid fibers or mixturemixtures thereof. By natural fiber, it is meant any of material of plantorigin or of animal origin. When used, the natural fibers are preferablyderived from vegetable sources such as for example from seed hair (e.g.cotton), stem plants (e.g. hemp, flax, bamboo; both bast and corefibers), leaf plants (e.g. sisal and abaca), agricultural fibers (e.g.,cereal straw, corn cobs, rice hulls and coconut hair) or lignocellulosicfiber (e.g. wood, wood fibers, wood flour, paper and wood-relatedmaterials). As mentioned above, more than one fibrous materials can beused. A combination of fibrous materials made of different fibers can beused such as for example a composite structure comprising one or morecentral layers made of glass fibers or natural fibers and one or moresurface layers made of carbon fibers or glass fibers. Preferably, thefibrous material is selected from woven structures, non-woven structuresand combinations thereof, wherein said structures are made of glassfibers and wherein the glass fibers are E-glass filaments with adiameter between 8 and 30 microns and preferably with a diameter between10 to 24 microns.

The fibrous material may further contain a thermoplastic material andthe materials described above, for example the fibrous material may bein the form of commingled or co-woven yarns or a fibrous materialimpregnated with a powder made of a thermoplastic material that issuited to subsequent processing into woven or non-woven forms, or amixture for use as a uni-directional material or a fibrous materialimpregnated with oligomers that will polymerize in situ duringimpregnation.

Preferably, the ratio between the fibrous material and the polymermaterials in the first component. i.e. the fibrous material incombination with the matrix resin composition and the surface resincomposition, is at least 30 volume percent fibrous material and morepreferably between 40 and 60 volume percent fibrous material, thepercentage being a volume-percentage based on the total volume of thefirst component.

The matrix resin composition is made of a thermoplastic resin that iscompatible with the surface resin composition. The surface resincomposition is selected from polyamide compositions comprising a blendof (A) one or more fully aliphatic group (I) polyamides having a meltingpoint of less than 230° C. and (B) one or more fully aliphaticpolyamides selected from group (II) polyamides having a melting point ofat least 250° C. The matrix resin composition is independently selectedfrom (B) or independently selected from blends of (A) and (B). Thematrix resin composition and the surface resin composition may beidentical or different. When the surface resin composition and thematrix resin composition are different, and when the matrix resincomposition is selected from blends of (A) and (B), it means that thecomponent (A), i.e. the one or more group (I) fully aliphatic polyamideshaving a melting point of less than 230° C., and/or the component (B),i.e. the one or more fully aliphatic polyamides selected from group (II)polyamides having a melting point of at least 250° C., are not the sameand/or that the amounts of component (A) and/or (B) are different in thesurface resin composition and the matrix resin composition.

Preferably, the matrix resin composition comprises a blend of (A) theone or more group (I) polyamides and (B) one or more polyamides selectedfrom group (II) polyamides in a weight ratio (A:B) from about 1:99 toabout 95:5, more preferably from about 15:85 to about 85:15. Still morepreferably the matrix resin composition comprises a blend of (A) the oneor more group (I) polyamides and (B) one or more polyamides selectedfrom group (II) polyamides in a weight ratio (A:B) from about 20:80 toabout 30:70, or is selected solely from one or more polyamides B.

Preferably, the surface resin composition comprises a blend of (A) theone or more group (I) polyamides and (B) one or more polyamides selectedfrom group (II) polyamides (B) in a weight ratio (A:B) from about 1:99to about 95:5, more preferably from about 15:85 to about 85:15, andstill more preferably 40:60 to about 60:40.

Polyamides are condensation products of one or more dicarboxylic acidsand one or more diamines, and/or one or more aminocarboxylic acids,and/or ring-opening polymerization products of one or more cycliclactams.

The one or more fully aliphatic polyamides (A) and (B) are formed fromaliphatic and alicyclic monomers such as diamines, dicarboxylic acids,lactams, aminocarboxylic acids, and their reactive equivalents. Asuitable aminocarboxylic acid is 11-aminododecanoic acid. Suitablelactams include caprolactam and laurolactam. In the context of thisinvention, the term “fully aliphatic polyamide” also refers tocopolymers derived from two or more such monomers and blends of two ormore fully aliphatic polyamides. Linear, branched, and cyclic monomersmay be used. Carboxylic acid monomers comprised in the fully aliphaticpolyamides are aliphatic carboxylic acids, such as for example adipicacid (C6), pimelic acid (C7), suberic acid (C8), azelaic acid (C9),sebacic acid (C10), dodecanedioic acid (C12) and tetradecanedioic acid(C14). Preferably, the aliphatic dicarboxylic acids of the one or morefully aliphatic polyamides (A) and (B) are selected from adipic acid anddodecanedioic acid. The one or more fully aliphatic polyamides (A) and(B) described herein comprise an aliphatic diamine as previouslydescribed. Preferably, the one or more diamine monomers of the one ormore fully aliphatic polyamide copolymer (A) and (B) according to thepresent invention are selected from tetramethylene diamine andhexamethylene diamine. Suitable examples fully aliphatic polyamidesinclude polyamide 6; polyamide 6,6; polyamide 4,6; polyamide 6,10;polyamide 6,12; polyamide 6,14; polyamide 6,13; polyamide 6,15;polyamide 6,16; polyamide 11; polyamide 12; polyamide 9,10; polyamide9,12; polyamide 9,13; polyamide 9,14; polyamide 9,15; polyamide 6,16;polyamide 9,36; polyamide 10,10; polyamide 10,12; polyamide 10,13;polyamide 10,14; polyamide 12,10; polyamide 12,12; polyamide 12,13;polyamide 12,14. Preferred examples of fully aliphatic polyamides (B)useful in the polyamide composition of the present invention arepoly(hexamethylene adipamide) (polyamide 66, PA66, also called nylon66), and poly(tetramethylene adipamide) (polyamide 46, PA46, also callednylon 46).

Preferred group (I) polyamides having a melting point of less than 230°C. comprise a fully aliphatic polyamide selected from the groupconsisting of poly(ε-caprolactam) (PA 6), and poly(pentamethylenedecanediamide) (PA510), poly(pentamethylene dodecanediamide) (PA512),poly(ε-caprolactam/hexamethylene hexanediamide) (PA6/66),poly(ε-caprolactam/hexamethylene decanediamide) (PA6/610),poly(ε-caprolactam/hexamethylene dodecanediamide) (PA6/612),poly(hexamethylene tridecanediamide) (PA613), poly(hexamethylenepentadecanediamide) (PA615), poly(ε-caprolactam/hexamethylenehexanediamide/hexamethylene decanediamide) (PA6/66/610),poly(ε-caprolactam/hexamethylene hexanediamide/hexamethylenedodecanediamide) (PA6/66/612), poly(ε-caprolactam/hexamethylenehexanediamide/hexamethylene decanediamide/hexamethylene dodecanediamide)(PA6/66/610/612), poly(2-methylpentamethylenehexanediamide/hexamethylene hexanediamide/) (PA D6/66),poly(decamethylene decanediamide) (PA1010), poly(decamethylenedodecanediamide) (PA1012), poly(11-aminoundecanamide) (PA11),poly(12-aminododecanamide) (PA12), PA6,12, PA12,12.

Preferred group (II) polyamides having a melting point of at least 250°C., are polyamides selected from the group poly(hexamethylenehexanediamide) (PA 66), poly(ε-caprolactam/hexamethylene hexanediamide)(PA6/66), (PA6/66/610), poly(ε-caprolactam/hexamethylenehexanediamide/hexamethylene dodecanediamide) (PA6/66/612),poly(ε-caprolactam/hexamethylene hexanediamide/hexamethylenedecanediamide/hexamethylene dodecanediamide) (PA6/66/610/612),poly(2-methylpentamethylene hexanediamide/hexamethylene hexanediamide/)(PA D6/66), poly(tetramethylene hexanediamide) (PA46).

An embodiment of the current invention comprises a matrix resincomposition and a surface resin composition comprising PA6 (group (I)polyamide A) and PA66 (group (II) polyamide B) in an A:B ratio of 25:75.

A preferred embodiment of the current invention comprise a matrix resincomposition comprising PA6 (group (I) polyamide A) and PA66 (group (II)polyamide B) in a A:B ratio of 25:75 and a surface resin compositioncomprising PA6 (group (I) polyamide A) and PA66 (group (II) polyamide B)in an A:B ratio of 50:50.

Another preferred embodiment of the current invention comprise a matrixresin composition comprising PA66 (group (II) polyamide B) and a surfaceresin composition comprising PA6 (group (I) polyamide A) and PA66 (group(II) polyamide B) in an A:B ratio of 50:50.

The surface resin composition described herein and/or the matrix resincomposition may further comprise one or more impact modifiers, one ormore heat stabilizers, one or more oxidative stabilizers, one or moreultraviolet light stabilizers, one or more flame retardant agents ormixtures thereof.

The surface resin composition described herein and/or the matrix resincomposition may further comprise one or more reinforcing agents such asglass fibers, glass flakes, carbon fibers, carbon nanotubes, mica,wollastonite, calcium carbonate, talc, calcined clay, kaolin, magnesiumsulfate, magnesium silicate, boron nitride, barium sulfate, titaniumdioxide, sodium aluminum carbonate, barium ferrite, and potassiumtitanate. When present, the one or more reinforcing agents are presentin an amount from at or about 1 to at or about 60 wt-%, preferably fromat or about 1 to at or about 40 wt-%, or more preferably from at orabout 1 to at or about 35 wt-%, the weight percentages being based onthe total weight of the surface resin composition or the matrix resincomposition, as the case may be.

As mentioned above, the matrix resin composition and the surface resincomposition may be identical or different. With the aim of increasingthe impregnation rate of the fibrous material, the melt viscosity of thecompositions may be reduced and especially the melt viscosity of thematrix resin composition.

The surface resin composition described herein and/or the matrix resincomposition may further comprise modifiers and other ingredients,including, without limitation, flow enhancing additives, lubricants,antistatic agents, coloring agents (including dyes, pigments, carbonblack, and the like), nucleating agents, crystallization promotingagents and other processing aids known in the polymer compounding art.

Fillers, modifiers and other ingredients described above may be presentin the composition in amounts and in forms well known in the art,including in the form of so-called nano-materials where at least one ofthe dimensions of the particles is in the range of 1 to 1000 nm.

Preferably, the surface resin compositions and the matrix resincompositions are melt-mixed blends, wherein all of the polymericcomponents are well-dispersed within each other and all of thenon-polymeric ingredients are well-dispersed in and bound by the polymermatrix, such that the blend forms a unified whole. Any melt-mixingmethod may be used to combine the polymeric components and non-polymericingredients of the present invention. For example, the polymericcomponents and non-polymeric ingredients may be added to a melt mixer,such as, for example, a single or twin-screw extruder; a blender; asingle or twin-screw kneader; or a Banbury mixer, either all at oncethrough a single step addition, or in a stepwise fashion, and thenmelt-mixed. When adding the polymeric components and non-polymericingredients in a stepwise fashion, part of the polymeric componentsand/or non-polymeric ingredients are first added and melt-mixed with theremaining polymeric components and non-polymeric ingredients beingsubsequently added and further melt-mixed until a well-mixed compositionis obtained.

Depending on the end-use application, the composite structure accordingto the present invention may have any shape. In a preferred embodiment,the composite structure according to the present invention is in theform of a sheet structure. The composite structure may be flexible, inwhich case it can be rolled.

The composite structure can be made by a process that comprises a stepof impregnating the fibrous material with the matrix resin composition,wherein at least a portion of the surface of the composite structure, ismade of the surface resin composition. Preferably, the fibrous materialis impregnated with the matrix resin by thermopressing. Duringthermopressing, the fibrous material, the matrix resin composition andthe surface resin composition undergo heat and pressure in order toallow the resin compositions to melt and penetrate through the fibrousmaterial and, therefore, to impregnate said fibrous material.

Typically, thermopressing is made at a pressure between 2 and 100 barsand more preferably between 10 and 40 bars and a temperature which isabove the melting point of the matrix resin composition and the surfaceresin composition, preferably at least about 20° C. above the meltingpoint to enable a proper impregnation. Heating may be done by a varietyof means, including contact heating, radiant gas heating, infra redheating, convection or forced convection air heating, induction heating,microwave heating or combinations thereof.

The impregnation pressure can be applied by a static process or by acontinuous process (also known as dynamic process), a continuous processbeing preferred for reasons of speed. Examples of impregnation processesinclude without limitation vacuum molding, in-mold coating, cross-dieextrusion, pultrusion, wire coating type processes, lamination,stamping, diaphragm forming or press-molding, lamination beingpreferred. During lamination, heat and pressure are applied to thefibrous material, the matrix resin composition and the surface resincomposition through opposing pressured rollers or belts in a heatingzone, preferably followed by the continued application of pressure in acooling zone to finalize consolidation and cool the impregnated fibrousmaterial by pressurized means. Examples of lamination techniques includewithout limation calendering, flatbed lamination and double-belt presslamination. When lamination is used as the impregnating process,preferably a double-belt press is used for lamination.

Should the matrix resin composition and the surface resin composition bedifferent, the surface resin composition always faces the environment ofthe first component so as to be accessible when the overmolding resincomposition is applied onto the composite structure.

The matrix resin composition and the surface resin composition areapplied to the fibrous material by conventional means such as forexample powder coating, film lamination, extrusion coating or acombination of two or more thereof, provided that the surface resincomposition is applied on at least a portion of the surface of thecomposite structure, which surface is exposed to the environment of thefirst component.

During a powder coating process, a polymer powder which has beenobtained by conventional grinding methods is applied to the fibrousmaterial. The powder may be applied onto the fibrous material byscattering, sprinkling, spraying, thermal or flame spraying, orfluidized bed coating methods. Optionally, the powder coating processmay further comprise a step which consists in a post sintering step ofthe powder on the fibrous material. The matrix resin composition and thesurface resin composition are applied to the fibrous material such thatat least a portion of the surface of the first component is made of thesurface resin composition. Subsequently, thermopressing is performed onthe powder coated fibrous material, with an optional preheating of thepowder coated fibrous material outside of the pressurized zone.

During film lamination, one or more films made of the matrix resincomposition and one or more films made of the surface resin compositionwhich have been obtained by conventional extrusion methods known in theart such as for example blow film extrusion, cast film extrusion andcast sheet extrusion are applied to the fibrous material, e.g. bylayering. Subsequently, thermopressing is performed on the assemblycomprising the one or more films made of the matrix resin compositionand the one or more films made of the surface resin composition and theone or more fibrous materials. In the resulting first component, thefilms melt and penetrate around the fibrous material as a polymercontinuum surrounding the fibrous material.

During extrusion coating, pellets and/or granulates made of the matrixresin composition and pellets and/or granulates made of the surfaceresin composition are melted and extruded through one or more flat diesso as to form one or more melt curtains which are then applied onto thefibrous material by laying down the one or more melt curtains.Subsequently, thermopressing is performed on the assembly comprising thematrix resin composition, the surface resin composition and the one ormore fibrous materials.

Depending on the end-use application, the composite structure obtainedunder step i) may be shaped into a desired geometry or configuration, orused in sheet form. The process for making a composite structureaccording to the present invention may further comprise a step ii) ofshaping the composite structure, said step arising after theimpregnating step i). The step of shaping the composite structureobtained under step i) may be done by compression molding, stamping orany technique using heat and/or pressure. Preferably, pressure isapplied by using a hydraulic molding press. During compression moldingor stamping, the composite structure is preheated to a temperature abovethe melt temperature of the surface resin composition and is transferredto a forming or shaping means such as a molding press containing a moldhaving a cavity of the shape of the final desired geometry whereby it isshaped into a desired configuration and is thereafter removed from thepress or the mold after cooling to a temperature below the melttemperature of the surface resin composition and preferably below themelt temperature the matrix resin composition.

The composite structure of the invention is particularly suited toovermolding with a polyamide overmolding resin composition. Anypolyamide resin can be used for the overmolding resin composition.Particularly good adhesion is obtained when the overmolding resincomposition is selected from polyamide compositions selected from (B) orindependently selected from polyamide compositions comprising a blend of(A) one or more fully aliphatic polyamides selected from group (I)polyamides having a melting point of less than 230° C., and (B) one ormore fully aliphatic polyamides selected from group (II) polyamideshaving a melting point of at least 250° C.

The composite structures according to the present invention may be usedin a wide variety of applications such as for example as components forautomobiles, trucks, commercial airplanes, aerospace, rail, householdappliances, computer hardware, hand held devices, recreation and sports,structural component for machines, structural components for buildings,structural components for photovoltaic equipments or structuralcomponents for mechanical devices.

Examples of automotive applications include without limitation seatingcomponents and seating frames, engine cover brackets, engine cradles,suspension arms and cradles, spare tire wells, chassis reinforcement,floor pans, front-end modules, steering column frames, instrumentpanels, door systems, body panels (such as horizontal body panels anddoor panels), tailgates, hardtop frame structures, convertible top framestructures, roofing structures, engine covers, housings for transmissionand power delivery components, oil pans, airbag housing canisters,automotive interior impact structures, engine support brackets, crosscar beams, bumper beams, pedestrian safety beams, firewalls, rear parcelshelves, cross vehicle bulkheads, pressure vessels such as refrigerantbottles and fire extinguishers and truck compressed air brake systemvessels, hybrid internal combustion/electric or electric vehicle batterytrays, automotive suspension wishbone and control arms, suspensionstabilizer links, leaf springs, vehicle wheels, recreational vehicle andmotorcycle swing arms, fenders, roofing frames and tank flaps.

Examples of household appliances include without limitation washers,dryers, refrigerators, air conditioning and heating. Examples ofrecreation and sports include without limitation inline-skatecomponents, baseball bats, hockey sticks, ski and snowboard bindings,rucksack backs and frames, and bicycle frames. Examples of structuralcomponents for machines include electrical/electronic parts such as forexample housings for hand held electronic devices, computers.

EXAMPLES

The following materials were used for preparing the compositesstructures according to the present invention and comparative examples.

Materials

The materials below are comprised in the compositions used in theExamples and Comparative Examples.

Polyamide from group II (B)(PA1 in Tables 1 and 2): a group II polyamidemade of adipic acid and 1,6-hexamethylenediamine with a weight averagemolecular weight of around 32000 Daltons. PA1 has a melting point ofabout 260° C. to about 265° C. and a glass transition of about 40° C. toabout 70° C. PA1 is called PA6,6 and is commercially available, forexample, from E. I. du Pont de Nemours and Company.

Polyamide from group I (A) (PA2 in Tables 1 and 2): a group I polyamidemade of ε-caprolactam having a melting point of about 220° C. PA2 iscalled PA6 and is commercially available, for example, from BASFcorporation.

Preparation of Films

The resin compositions used in the Examples (abbreviated as “E” inTables 1 and 2), and Comparative Example (abbreviated as “C” in Tables 1and 2) were prepared by melting or melt-blending the ingredients in atwin-screw extruder at about 280° C. Upon exiting the extruder throughan adaptor and a film die at about 280° C., the compositions were castonto a casting drum at about 100° C. into about 102 micron thick film inthe case of the matrix resin compositions of C1, E1, and E2 (Table 1)and the surface resin composition of C1 (Table 1), about 200 micronthick films in the case of the surface resin composition of Examples E1and E2 (Table 1), and about 250 micron thick films in the case of bothmatrix and surface resin compositions of E3 and C2 (Table 2). Thethickness of the films was controlled by the rate of drawing.

Preparation of the Composite Structures E1, E2, and C1 of Table 1

The composite structures C1 (comparative), E1, and E2 were prepared byfirst making a laminate by stacking eight layers having a thickness ofabout 102 microns and made of PA1 and three layers of woven continuousglass fiber textile (E-glass fibers having a diameter of 17 microns,0.4% of a silane-based sizing and a nominal roving tex of 1200 g/km thathave been woven into a 2/2 twill (balanced weave) with an areal weightof 600 g/m²) in the following sequence: two layers made of PA1, onelayer of woven continuous glass fiber textile, two layers of PA1, onelayer of woven continuous glass fiber textile, two layers of PA1, onelayer of woven continuous glass fiber textile and two layers of PA1.

The laminates were prepared using an isobaric double press machine withcounter rotating steel belts, both supplied by Held GmbH. The differentfilms enterered the machine from unwinders in the previously definedstacking sequence. The heating zones were about 2000 mm long and thecooling zones were about 1000 mm long. Heating and cooling weremaintained without release of pressure. The laminates were prepared withthe following conditions: a lamination rate of 1 m/min, a maximummachine temperature of 360° C. and laminate pressure of 40 bar. Theso-obtained laminates had an overall thickness of about 1.5 mm.

Films of about 200 micrometers and made of the surface polyamide resincompositions of E1 and E2 described in Table 1 were applied to the abovedescribed laminate, forming the composite structure. The filmscomprising the surface polyamide resin compositions were made with a 28mm W&P extruder with an adaptor and film die and an oil heated castingdrum. The extruder and adaptor and die temperatures were set at 280° C.,and the temperature of the casting drum was set at 100° C. The compositestructures were formed by compression molding the films by a Dake Press(Grand Haven, Mich.) Model 44-225 (pressure range 0-25K) with an 8 inchplatten. A 6×6″ specimen of the laminate was placed in the mold and thefilm was pressed onto the laminate's surface at a tempertature of about300° C. and with a pressure of about 3 KPsi for about 2 minutes, andwith a pressure of about 6 Kpsi for about 3 additional minutes andsubsequently cooled to room temperature. The composite structurescomprising a surface made of the surface polyamide resin compositions ofE1 or E2 described in Table 1, the matrix resin compositions PA1 and thefibrous material had an overall thickness of about 1.5 mm.

Preparation of the Composite Structures E3 and C2 of Table 2

Preparation of the composite structures E3 and C2 in Table 2 wasaccomplished by laminating multiple layers of film of compositions shownin Table 2 and woven continuous glass fiber textile (prepared fromE-glass fibers having a diameter of 17 microns, sized with 0.4% of asilane-based sizing agent and a nominal roving tex of 1200 g/km thathave been woven into a 2/2 twill (balanced weave) with an areal weightof 600 g/m²) in the following sequence: two layers of film of surfaceresin composition, one layer of woven continuous glass fiber textile,two layers of film of matrix resin composition, one layer of wovencontinuous glass fiber textile, two layers of film of matrix resincomposition, one layer of woven continuous glass fiber textile, and twolayers of film of surface resin composition.

The composite structures of table 2 were compression molded by a DakePress (Grand Haven, Mich.) Model 44-225, Pressure range 0-25K, with an 8inch platten. A 6×6″ specimen of film and glass textile layers asdescribed above was placed in the mold and heated to a temperature ofabout 320° C., held at the temperature for 2 minutes without pressure,then pressed at the 320° C. temperature with the following pressures:about 6 bar for about 2 minutes, then with about 22 bar for about 2additional minutes, and then with about 45 bar for about 2 additionalminutes; they were subsequently cooled to ambient temperature. Thethusly formed composite structures had a thickness of about 1.6 mm.

Bond Strength of Composite Structures C1, E1, and E2 of Table 1

When composite structures C1, E1, and E2 were over-injection molded withan overmolding resin composition comprising PA1 and 30 weight percent ofglass fibers (percentage of the total composition of the overmoldingresin), the bond strengths were respectively 0, 86, and 121 MPa,demonstrating the superior ability of a blend of polyamide selected fromgroup 1 with polyamide selected from group II to form strong bondstrength to an overmolding resin, when compared to a polyamide from onesingle group of polyamides.

The over-injection molding was accomplished by over-injection molding1.7 mm of the overmolding resin composition onto the compositestructures obtained as described above. The composite structures C1, E1,and E2 comprising a surface made of the surface resin compositionslisted in Table 1, the matrix resin compositions listed in Table 1 andthe fibrous material described above were cut into 5×5″ (about 127mm×127 mm) specimens and placed into a heating chamber for 3 min at 180°C. Then the composite structures were quickly transferred with a robotarm into a mold cavity of an Engel vertical press and were overinjection molded with the overmolding resin composition comprising PA1and 30 weight percent of glass fibers (percentage of the totalcomposition of the overmolding resin) by an Engel molding machine. Thetransfer time from leaving the heating chamber to contact with theovermolding resin was 9 sec. The mold was oil heated at 120° C. Theinjection machine was set at 280° C.

The 5×5″ specimens of the overmolded composite structures comprising E1,E2, and C1 prepared as described above, were cut into ¾“×5” testspecimens (about 19 mm×about 127 mm), and were notched by cutting theovermolded part up to the interface of the overmolded part and thecomposite structure. The notch was made through the width at about themiddle (lengthwise) of the test specimen. The bond strength of theovermolded resin composition to the composite structure was measured onthe notched test specimens via a 3 point bend method, modified ISO-178.The apparatus and geometry were according to ISO method 178, bending thespecimen with a 2.0″ (about 51 mm) support width with the loading edgeat the center of the span. The over-molded part of the specimen was onthe tensile side (outer span) resting on the two side supports (at 2″(about 51 mm) apart), while indenting with the single support (the load)on the compression side (inner span) on the composite structure of thespecimen. In this test geometry, the notch in the specimens was down(tensile side). The notch was placed ¼″ off center (¼″ away from theload). The tests were conducted at 2 mm/min. The test was run until aseparation or fracture between the two parts of the specimen(delamination) was seen. The stress at that point was recorded.

Flexural Strength of Composite Structures E3 and C2 in Table 2

The composite structures E3 and C2 in Table 2 were cut into ½″ (about12.7 mm) by 2.5″ (about 64 mm) long test specimens (bars) using a MK-377Tile Saw with a diamond edged blade and water as a lubricant. FlexuralStrength was tested on the test specimens via a 3-point bend test. Theapparatus and geometry were according to ISO method 178, bending thespecimen with a 2.0″ support width with the loading edge at the centerof the span. The tests were conducted with 1 KN load at 2 mm/min untilfracture. The results are shown in Table 2, 380 and 332 MPa forcomposite structures E3 and C2 respectively, demonstrating the superiorflexural strength of a composite structure made of a blend of polyamideselected from group 1 with polyamide selected from group II, whencompared to a composite structure made of a polyamide from one singlegroup of polyamides.

TABLE 1 Composite Composite Composite structure structure structure C1E1 E2 Matrix resin 100 wt-% PA1 100 wt-% PA1 100 wt-% PA1 compositionSurface resin 100 wt-% PA1 blend of: blend of: composition 75 wt-% ofPA1 and 50 wt-% of PA1 and 25 wt-% of PA2 50 wt-% of PA2

TABLE 2 E3 C2 Matrix Resin Composition PA1 50 100 PA2 50 Surface ResinComposition PA1 50 100 PA2 50 ISO-178 3 Point Flex Flexural Strength atBreak (Mpa) 380 332

1. A composite structure having a surface, which surface has at least aportion made of a surface resin composition, and comprising a fibrousmaterial selected from the group consisting of non-woven structures,textiles, fibrous battings and combinations thereof, said fibrousmaterial being impregnated with a matrix resin composition, wherein thesurface resin composition is selected from polyamide compositionscomprising a blend of (A) one or more fully aliphatic polyamidesselected from group (I) polyamides having a melting point of less than230° C., and (B) one or more fully aliphatic polyamides selected fromgroup (II) polyamides having a melting point of at least 250° C., andwherein the matrix resin composition is independently selected from (B)or independently selected from blends of (A) and (B).
 2. The compositestructure according to claim 1, wherein the fibrous material is made ofglass fibers, carbon fibers, aramid fibers, natural fibers or mixturesthereof.
 3. The composite structure according to claim 2, wherein thefibrous material is made of glass fibers.
 4. The composite structureaccording to claim 1 wherein the fibrous material is from 30 volumepercent to 60 volume percent of the composite structure.
 5. Thecomposite structure according to claim 1 further comprising one or moreadditives selected from the group consisting of heat stabilizers,oxidative stabilizers, reinforcing agents and flame retardants orcombination thereof.
 6. The composite structure according claim 1wherein the one or more fully aliphatic polyamides selected from group(I) polyamides is selected form the group consisting of PA 6, PA510,PA512, PA6/66, PA6/610, PA6/612, PA613, PA615, PA6/66/610, PA6/66/612,PA6/66/610/612, PA D6/66, PA1010, PA1012, PA11, PA12, PA612, PA1212. 7.The composite structure according to claim 1 wherein the one or morefully aliphatic polyamides selected from group (II) polyamides isselected form the group consisting of PA 66, PA6/66, PA6/66/610,PA6/66/612, PA6/66/610/612, PA D6/66, PA46.
 8. The composite structureaccording to claim 1 wherein the weight ratio of the one or morepolyamides selected from group (I) polyamides (A) and the one or morepolyamides selected from group (II) polyamides (B) (A:B) of the matrixpolyamide composition and of the surface polyamide composition isbetween from about 1:99 to about 95:5.
 9. The composite structureaccording claim 1 wherein the weight ratio of the one or more polyamidesselected from group (I) polyamides (A) and the one or more polyamidesselected from group (II) polyamides (B) (A:B) of the matrix polyamidecomposition is from about 20:80 to about 30:70.
 10. The compositestructure according claim 1 wherein the weight ratio of the one or morepolyamides selected from group (I) polyamides (A) and the one or morepolyamides selected from group (II) polyamides (B) (A:B) of the surfacepolyamide composition is from about 20:80 to about 60:40.
 11. Thecomposite structure according to claim 1 wherein group (I) polyamides(A) comprises PA6, PA6/12, PA10/10 solely or in combinations thereof.12. The composite structure according to claim 1 wherein group (II)polyamides (B) comprises PA66, PA46, solely or in combinations thereof.13. The composite structure according to claim 1 in the form of acomponent for automobiles, trucks, commercial airplanes, aerospace,rail, household appliances, computer hardware, hand held devices,recreation and sports, structural component for machines, structuralcomponents for buildings, structural components for photovoltaicequipments or structural components for mechanical devices.
 14. Aprocess for making the composite structure of claim 1 having a surface,said process comprises a step of: i) impregnating with a matrix resincomposition a fibrous material selected from non-woven structures,textiles, fibrous battings and combinations thereof, said fibrousmaterial being impregnated with a matrix resin composition, wherein atleast a portion of the surface of the composite structure is made of asurface resin composition, and wherein the surface resin composition isselected from polyamide compositions comprising a blend of (A) one ormore fully aliphatic polyamides selected from group (I) fully aliphaticpolyamides having a melting point of less than 230° C.; and (B) one ormore fully aliphatic polyamides selected from group (II) polyamideshaving a melting point of at least 250° C., and wherein the matirx resincomposition is indepedently selected from (B) or independently selectedfrom blends of (A) and (B).